For a man at the center of one of the most politically sensitive criminal investigations ever undertaken, Judge Ilario Martella has made remarkably few known enemies.

Martella, 49, who has spent the past three years investigating the plot to kill Pope John Paul II, has the reputation of being one of Italy's most respected and conscientious magistrates. Quiet and unassuming, he has sought to avoid personal publicity and to steer clear of controversy.

Now that his job is over, with the submission in court of a 1,243-page indictment of three Bulgarians and four Turks as the alleged accomplices of would-be assassin Mehmet Ali Agca, Martella replies to requests for formal interviews by saying courteously that he is tired and would like to get some rest.

The full text of the judge's final report, which will form the basis of a potentially sensational criminal trial, has not been published. The partial text released Friday, as well as Martella's public comments on the indictment, seem to reflect his cautious nature.

He has said that he has not felt able to go as far as the public prosecutor, Antonio Albano, who depicts the assassination attempt as a Soviet Bloc conspiracy designed to suppress social and political upheavals in the pope's native Poland. Martella also has insisted repeatedly that the guilt or innocence of the accused will be determined in open court.

Under the Italian judicial system, an examining magistrate such as Martella performs the role of an American police investigator and grand jury rolled into one. It is his job both to conduct the criminal investigation and to decide whether there is sufficient evidence to justify a trial.

In three years of pursuing the men who plotted to kill the pope, Martella has won plaudits from many different quarters for his fair-mindedness and attention to detail. There has been occasional criticism that he has difficulty reaching a firm decision and lacks imagination and intuitive insight. There have been no attacks, however, on his personal honesty or integrity.

Friends speak of Martella's sense of duty and his unwillingness to criticize colleagues. This year, he gave up his summer vacation -- an almost sacrosanct institution for Italians -- to work on his report.

The formal filing of the report in court was delayed as Martella reportedly agonized over the details of a complex plot ranging over half a dozen different countries.

Martella's handling of the case seems to have won him the grudging respect of the Bulgarian side. The official Bulgarian media have attacked prosecutor Albano and have questioned the impartiality of the Italian judiciary, but they have refrained from directly criticizing Martella.

"We feel that Martella has played according to the rules," a Bulgarian official in Rome said privately. "Since he has been on this case, we have never heard him make statements or release documents that are supposed to be secret. Unlike Albano, who gave interviews making all sorts of allegations about Bulgaria, Martella has behaved correctly."

Before formally submitting his report in court on Friday, Martella paid a courtesy call on the Bulgarian ambassador in Rome to notify him of his decision to indict two former members of his embassy and the deputy Rome station manager of the Bulgarian state airlines.

Lawyers involved in the case say that Martella has maintained an attitude of aloof impartiality. In contrast to many Italian judges, he does not seem to have pronounced political views. Socially, he avoids the world of magistrates and lawyers.

"The man appears to be incorruptible," said a senior Italian Communist Party official with some admiration.

Martella owed his early reputation to his investigation of a bribery scandal involving the American aircraft firm Lockheed and Italian politicians. Unlike many Italian scandals, which tend to begin in a blaze of publicity and peter out inconclusively, this one ended with a conviction of a Cabinet minister.

Martella was appointed to open a new investigation into a possible plot to kill the pope in November 1981 after another Italian judge rejected Agca's claim to have acted alone. His life changed dramatically as he became the focus of international media attention and was accompanied everywhere he went by armed bodyguards.

The investigation proceeded slowly in the early months, with Agca refusing to elaborate on his rather vague intitial statement. The turning point came in May 1982, a year after the assassination attempt, when the pope's would-be assassin started talking about his alleged accomplices.

During the next year and a half, Martella spent hundreds of hours cross-examining Agca. The verbatim record of their conversations is among 25,000 pages of evidence that will not become available until the trial, which is expected to take place sometime next year.

Although he worked closely with prosecutor Albano in investigating the case, the views of the two magistrates did not always coincide. The prosecutor has consistently objected to rulings by Martella allowing Bulgarian airlines official Sergei I. Antonov to be placed under house arrest on medical grounds rather than being held in prison.

Antonov, the only one of the three Bulgarians in the hands of the Italian authorities, is reported to be suffering from the eating disorder anorexia nervosa.

Martella and Albano also differ over whether a second gunman fired on the pope in St. Peter's Square. Martella maintains that eyewitness testimony as well as ballistic evidence shows that a third shot was fired from a different angle than Agca's. There is no mention of this third shot in Albano's report.

The Italian newspaper La Stampa today quoted Martella as saying that he believed the second gunman must have been standing about 30 or 40 yards away from Agca.

Martella told La Stampa that Agca had testified that he would have continued to fire had he not been seized by someone next to him in the crowd. The person who helped save the pope's life is not known, Martella added, but according to La Stampa it could have been an American nun who helped police capture Agca.